Studies have continued during the past year on red cell preservation with emphasis on the collection of better data on the regeneration of phosphate metabolities by incubation of long-stored human red cells with various combinations and different concentrations of adenine, inosine, adenosine, pyruvate and inogranic phosphate. The effects of pH and time of incubation were measured. Similar studies were carried out using the deoxyribose analogs of inosine and adenosine. Use of the rabbit as a model for experiments related to red cell stroage has continued with analyses of the changes of red cell metabolites during the storage of rabbit blood at 4 degrees in CPD or in CPD-adenine. Rejuvenation studies on long-stored rabbit red cells have been done by incubations with inosine, adenine and adenosine.